The US electorate has spoken. The Republican party yesterday won a majority in the US Senate, meaning the party controls both chambers of Congress for the first time since 2005. That’s thrown the future of US climate policy into some doubt, as Republican voters and politicians are generally less concerned about the issue than their Democrat colleagues.

Last year, President Obama announced his climate action plan. The centrepiece of the policy is a new regulation requiring power plants to cut emissions 30 per cent by 2030, known as the clean power plan.

The Republican’s Senate leader-elect, Kentucky senator Mitch McConnell, describes the policy as “a massive, big-government boondoggle“, and has pledged to try and overturn it. There are a number of ways the Republicans may set about this.

The Republicans already controlled the House of Representatives. Yesterday they won an additional seven seats in the Senate, giving the party a majority. That means the Democrats do not have enough members of Congress to block such a move.

The Republicans may also add clauses to any legislation the Democrats and president really want passed, known as riders, with the aim curbing Obama’s plan.

If Obama’s clean power plan is rolled back, it could have serious implications for international climate negotiations. Lots of countries argue that they shouldn’t be expected to act until the US does as it has the world’s largest historical emissions. China’s approach to the climate negotiations has arguably softened since Obama announced his action plan.

If the climate plan was no longer in place, or significantly curbed, China and nations may be reluctant to commit to strong climate action. That would represent a big blow to negotiators’ chances of getting a new global climate deal in Paris.

Committee powers

The election result means Republican senators are set to become chairs of some prominent committees. That gives a high-profile platform to some politicians vehemently opposed to tackling climate change, as The Nation points out.

Climate skeptic committee chairs such as Inhofe, Ted Cruz, and Ron Johnson may also move to cut funding to those charged with implementing Obama’s climate plan, such as the Environmental Protection Agency.

Combined, the committee chairs make the Senate altogether less climate-friendly.

That could spook other governments in the run-up to next year’s international climate negotiations. If they don’t think the US’s more proactive approach to curbing emissions is going to last, they are less likely to agree to taking action themselves.

Keystone XL

The Republicans are also likely to try and push the approval of a new oil pipeline connecting the US to Canada’s tar sands.

Campaign group 350.org have campaigned heavily against the project, called Keystone XL. It says the pipeline could deliver 800,000 barrels of the “world’s dirtiest oil” to the US each day, pushing up emissions.

The Republicans have always been in favour of the pipeline, and a number of Democrats also approve. Now the Republican’s have a majority in the Senate, they can table a vote on the pipeline, something the previous Democrat leader Harry Reid had been avoiding.

Democrats that oppose the pipeline are now unlikely to have enough votes to block it. That means President Obama will either have to veto the project or give Keystone XL a permit.

If the US builds new fossil fuel infrastructure, it may be harder for it to persuade other countries to decarbonise their energy systems. The Intergovernmental Panel on Climate Change (IPCC) says fossil fuels need to be phased out by 2100 if the world is going to avoid temperatures rising more than two degrees above pre-industrial levels.

If the US approves the Keystone XL pipeline, it could look like the country is ignoring the IPCC’s advice, potentially creating political space for others to do the same.

Global issues

The US’s efforts to curb emissions and the world’s prospects of taking action are largely synonymous.

Those unsure of the Senate’s international influence need only to think back to 1997, when a Republican Senate refused to ratify the Kyoto Protocol. That decision meant the world’s only binding agreement to cut emissions was hamstrung from the start. Many say it never recovered.